Self Assessment Tax Return Checklist (England & Wales)

You are required to file a Self Assessment tax return with HMRC under the Taxes Management Act 1970 s.8 if you meet any of the following criteria in the relevant tax year. You were self-employed as a sole trader and your gross trading income exceeded £1,000 (below which the Trading Allowance under ITTOIA 2005 s.783B may exempt you). You were a partner in a business partnership. Your total taxable income exceeded £150,000 (the threshold below which PAYE alone may suffice was reduced from £100,000 in recent years). You received untaxed income of more than £2,500, for example from property letting, overseas employment, or casual work. You received savings or investment income of more than £10,000 before tax. You received income from dividends above the Dividend Allowance (£500 for 2024/25). You were a company director (unless your company is a non-profit and you received no pay or benefits). You had Capital Gains Tax to pay — for example, from selling shares, investment property, cryptocurrency, or other chargeable assets. You received income from abroad. You claimed expenses in excess of £2,500 as an employee. You were subject to the High Income Child Benefit Tax Charge because your adjusted net income exceeded £60,000. You or your partner had income above £60,000 and received Child Benefit. You received a P800 from HMRC indicating underpaid tax that cannot be collected through PAYE. You must register for Self Assessment by 5 October following the end of the tax year in which the obligation arose, under TMA 1970 s.7, or face a penalty.

Self Assessment deadlines are strictly enforced by HMRC under Schedule 55 of the Finance Act 2009. The paper tax return (SA100 and supplementary pages) must reach HMRC by 31 October following the end of the tax year — so for 2024/25 returns (6 April 2024 to 5 April 2025), the paper deadline is 31 October 2025. Online returns filed via Government Gateway have a later deadline of 31 January following the end of the tax year — for 2024/25, the online deadline is 31 January 2026. If you choose to file on paper, note that HMRC will not issue SA100 forms automatically; you must request them. For payment, all Income Tax, Class 4 NICs, and Capital Gains Tax due for the year must be paid by 31 January. If your tax bill exceeds £1,000 and less than 80% was collected via PAYE, you must also make Payments on Account under TMA 1970 s.59A: 50% of the prior year's liability is due on 31 January, and the remaining 50% on 31 July. Late filing penalties are automatic: £100 immediately after the deadline; daily penalties of £10 per day (up to £900) after 3 months; a further 5% of the tax due or £300 (whichever is greater) after 6 months; and a further 5% or £300 after 12 months. Late payment attracts interest at the official HMRC rate (currently Bank of England base rate + 2.5%) from the day after the deadline, plus 5% surcharges on unpaid tax at 30 days, 6 months, and 12 months after the January deadline under Schedule 56 FA 2009.

The legal obligation to keep Self Assessment records is set out in TMA 1970 s.12B and supplemented by HMRC's guidance. The retention period depends on the type of income you receive. For employees and individuals with straightforward investment income, records must be kept for at least 22 months after the end of the tax year to which they relate. For example, records for the 2024/25 tax year (ending 5 April 2025) must be kept until at least 31 January 2027. For self-employed individuals and those with property income, the retention period is 5 years and 10 months after the end of the tax year — so 2024/25 records must be retained until at least 31 January 2031. The categories of records you must retain include: all P60s, P45s, and P11D forms from employers; self-employment records including sales invoices, purchase receipts, mileage logs, bank statements, and stock records; property income records including rental agreements, letting agent statements, mortgage statements, and repair invoices; investment records including dividend vouchers, broker contract notes, and interest certificates; capital gains records including original purchase documents, improvement costs, and disposal documents; pension contribution certificates; Gift Aid declaration copies; and foreign income documentation. HMRC may open an enquiry into a Self Assessment return within 12 months of the filing date (TMA 1970 s.9A), but this can extend to 4 or 6 years in cases of incomplete disclosure, or up to 20 years in cases of deliberate understatement.

Self-employment profits for Income Tax and Class 4 National Insurance purposes are calculated as gross receipts (turnover) minus allowable business expenses under the Income Tax (Trading and Other Income) Act 2005. The fundamental rule is that an expense is only deductible if it is incurred 'wholly and exclusively' for the purposes of the trade under ITTOIA 2005 s.34. Dual-purpose expenditure — expenses that have both a business and personal element — is generally not deductible unless there is a clearly identifiable business portion. Common allowable expenses include: cost of goods sold and materials; employee wages and subcontractor costs; rent, rates, and utility costs for business premises; motor vehicle running costs (on the business-use proportion, or using the HMRC approved mileage rate of 45p per mile for the first 10,000 miles, 25p thereafter, under ITEPA 2003 s.229); marketing and advertising costs; professional fees (accountancy, legal, insurance); bank charges; subscriptions to professional bodies; and the cost of replacing small items of equipment. For businesses using the cash basis — available to unincorporated businesses with turnover up to £150,000 under ITTOIA 2005 s.25A — receipts and payments are recognised when cash is received or paid, simplifying record-keeping. Capital expenditure on business assets is not directly deductible but qualifies for capital allowances under the Capital Allowances Act 2001, including the Annual Investment Allowance (100% deduction up to £1 million per year) and Writing Down Allowances.

The High Income Child Benefit Tax Charge (HICBC) was introduced by the Finance Act 2012 (now codified in the Income Tax Act 2007 ss.681B–681H) and applies to individuals whose adjusted net income (ANI) exceeds £60,000 in a tax year (from 6 April 2024, raised from the previous £50,000 threshold). The charge operates as a tax on the Child Benefit received, calculated at 1% of the benefit for every £200 of ANI above £60,000. This means the charge equals 100% of the Child Benefit — effectively cancelling its value entirely — when ANI reaches £80,000 (for 2024/25). For ANI between £60,000 and £80,000, the charge is a tapered proportion of the Child Benefit amount. The charge applies to the higher earner of a couple, regardless of who actually receives the Child Benefit payments. For example, if one partner earns £70,000 ANI and they receive Child Benefit of £2,212 per year (for two children at 2024/25 rates), the charge is: (£70,000 − £60,000) ÷ £200 × 1% × £2,212 = 50% × £2,212 = £1,106. The charge is collected through the Self Assessment tax return (SA100, Question 2). Families may opt out of receiving Child Benefit to avoid the charge, but this forfeits the National Insurance credits the non-working parent receives (worth up to £5,839 per year of State Pension entitlement). For those who have not yet reported the HICBC for previous years, HMRC can assess up to 4 years back (or 6 years if there was careless behaviour).

Yes. Under TMA 1970 s.9ZA, you can amend a Self Assessment tax return at any time within 12 months of the filing deadline for the relevant year. For the 2024/25 tax year, with an online filing deadline of 31 January 2026, the amendment deadline is 31 January 2027. Amendments can be made online via Government Gateway or by writing to HMRC. Common reasons for amending a return include: receiving a late P60 or corrected P60 from an employer; discovering additional income sources after filing; realising an expense was omitted or incorrectly calculated; receiving a corrected P11D for benefits in kind; identifying an arithmetic error; or claiming an additional relief that was overlooked (such as higher-rate pension relief or Gift Aid relief). After the 12-month amendment window closes, you cannot amend the return yourself, but you may make an overpayment relief claim under TMA 1970 s.33 within four years of the end of the tax year, if you believe you have paid too much tax. HMRC may independently open an enquiry into your return under TMA 1970 s.9A within 12 months of the filing date (or later in cases of fraud or incomplete disclosure). If HMRC disagrees with your return following an enquiry, it may issue an amendment under TMA 1970 s.28A, which you can appeal to the First-tier Tribunal (Tax Chamber) within 30 days under TMA 1970 s.31. It is good practice to review your previous year's return before filing the current year, to identify any amendments needed and confirm consistency.